Java query an ArrayList of predefined object

Question

I have an ArrayList (inputList) that parse this data:

id,name,quantity
1,foo,10
2,bar,20
3,foo,10
4,bar,10
5,qwerty,1

Code:

...
List<FooRow> inputList = new ArrayList<FooRow>();
inputList = br.lines().map(mapToFooRow).collect(Collectors.toList());
...

public class FooRow{
private Integer id;
private String name;
private Integer value;
}

I want to create a collectors that return me a list with the count of value grouped by name:

name,value
foo,20
bar,30
qwerty,1

How can I create a class Collectors to do this in the lambda expression? Thanks.

Oleksandr Pyrohov · Accepted Answer · 2018-09-19 13:56:23Z

2

You can use Collectors.groupingBy and Collectors.summingInt:

Map<String, Integer> result =
    inputList.stream()
             .collect(Collectors.groupingBy(
                 FooRow::getName, Collectors.summingInt(FooRow::getValue)));

edited Sep 19, 2018 at 13:56

answered Sep 19, 2018 at 13:49

Oleksandr Pyrohov

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